From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id D22746B01F1 for ; Thu, 22 Apr 2010 12:13:16 -0400 (EDT) Message-ID: <4BD07594.9080905@redhat.com> Date: Thu, 22 Apr 2010 19:13:08 +0300 From: Avi Kivity MIME-Version: 1.0 Subject: Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview References: <20100422134249.GA2963@ca-server1.us.oracle.com 4BD06B31.9050306@redhat.com> <53c81c97-b30f-4081-91a1-7cef1879c6fa@default> In-Reply-To: <53c81c97-b30f-4081-91a1-7cef1879c6fa@default> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Dan Magenheimer Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, jeremy@goop.org, hugh.dickins@tiscali.co.uk, ngupta@vflare.org, JBeulich@novell.com, chris.mason@oracle.com, kurt.hackel@oracle.com, dave.mccracken@oracle.com, npiggin@suse.de, akpm@linux-foundation.org, riel@redhat.com List-ID: On 04/22/2010 06:48 PM, Dan Magenheimer wrote: >>> a synchronous concurrency-safe page-oriented pseudo-RAM device (such >>> : >>> conform to certain policies as follows: >>> >> How baked in is the synchronous requirement? Memory, for example, can >> be asynchronous if it is copied by a dma engine, and since there are >> hardware encryption engines, there may be hardware compression engines >> in the future. >> > Thanks for the comment! > > Synchronous is required, but likely could be simulated by ensuring all > coherency (and concurrency) requirements are met by some intermediate > "buffering driver" -- at the cost of an extra page copy into a buffer > and overhead of tracking the handles (poolid/inode/index) of pages in > the buffer that are "in flight". This is an approach we are considering > to implement an SSD backend, but hasn't been tested yet so, ahem, the > proof will be in the put'ing. ;-) > Well, copying memory so you can use a zero-copy dma engine is counterproductive. Much easier to simulate an asynchronous API with a synchronous backend. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org